The objectives of this proposal are to investigate the intestinal absorption and transport of bile acid in the developing neonate. Intestinal perfusion studies of isolated segments of proximal jejunum and distal ileum will be performed in the neonatal animal model in order to characterize the mechanisms for bile salt absorption from the immature intestine. The ontogeny of a specific enzymatic marker, tryptophan oxygenase, previously identified in the distal ileum of the adult, will be characterized. The permeability of the developing intestine to an inert water soluble low molecular weight polyethylene glycol (PEG 400) will be validated and utilized as a probe to characterize intestinal permeability and as a marker to detect injury in the developing intestine. In addition to definition of the normal maturational sequences for bile salt absorption, specific pharmarcological intervention will be utilized in order to accelerate the maturation of intestinal function required to establish the mature levels of gastrointestinal function required to establish adequate lipid absorption in the immature infant.